Re: [PATCH v2 0/4] Enable SMEP CPU Feature

From: Ingo Molnar
Date: Tue May 17 2011 - 07:39:51 EST

* Avi Kivity <avi@xxxxxxxxxx> wrote:

> On 05/17/2011 01:46 PM, Ingo Molnar wrote:
> >>
> >> We could support it as a non-default feature, but that reduces its utility.
> >
> >It would be a nice touch for tools/kvm/: we would use KVM_GET_SREGS and
> >KVM_GET_SREGS to twiddle CR4.SMEP, even without the guest explicitly doing it.
> >
> >A quick glance suggests that it could be done straight away in
> >tools/kvm/kvm-cpu.c::kvm_cpu__setup_sregs() during vcpu setup, and hopefully
> >that cr4 value survives boot and ends up in the guest kernel's mmu_cr4_features
> >mask shadow register.
> Depends if the guest uses a read-modify-write pattern or not. We could do it
> transparently in kvm.ko, since the real cr4 need not corresponds to the guest
> notion (for example, we often set cr0.wp or cr0.ts even though the guest
> wants them clear).

Oh, being transparent is a nice touch when it comes to security measures
(catching attackers who think there's no SMEP and such) - but that would need
KVM support and a new ioctl to configure it, right?


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